1. Field of the Invention
The present invention relates to a light amount measuring apparatus which receives light and measures light amount of the received light.
2. Description of the Related Art
In recent years, the use of the light amount measuring apparatus for measuring light amount of the received light having predetermined wavelengths (e.g., wavelengths included in sunlight wavelengths) is widespread. For example, Japanese Patent Application Kokai Publication No. 2005-337827 (patent document 1) discloses an illuminance sensor including a photodiode that has sensitivity to both visible light and infrared light and an optical filter that is disposed on a light incident surface of the photodiode and blocks infrared light. In this sensor, the photodiode is reverse-biased by the power supply in order to measure light amount of the received light.
Furthermore, Japanese Patent Application Kokai Publication No. 2006-332226 (patent document 2) discloses a semiconductor photosensor device including a couple of photodiodes formed on a silicon substrate and an infrared transmitting filter that is disposed on one of the photodiodes and blocks visible light. In this device, both photodiodes are reverse-biased by the power supply in order to measure light amount of the received light, and the light amount of visible light is obtained by calculating deference between the outputs of the photodiodes.
However, in the device of patent document 1 or 2, since the photodiode or photodiodes are directly connected to the power supply, even if the device is set to an OFF-state, a comparatively large consumption current corresponding to light amount of the received light is generated in the photodiode or photodiodes when it receives light. Accordingly, there is a problem that electric power consumption exists due to the photodiode which is being irradiated with light, even when the device is in OFF-state.